Ultralytics YOLO

🌟 Summary

Ultralytics v8.4.21 improves reliability for Rockchip RKNN exports (main change) and also adds better tuning isolation, expanded C++ pose example support, and clearer YOLO26 optimizer guidance. 🚀

📊 Key Changes

• ✅ Main priority (PR #23806 by @Laughing-q): RKNN export path fix

  • RKNN filename generation was refactored to use safer path handling (Path(...).stem) instead of fragile string replacement.
  • Export output naming is now cleaner and more consistent, especially for unusual file names/paths.
  • Version bumped from 8.4.20 → 8.4.21.

• 🧪 Ray Tune reliability improvement (PR #23793 by @Y-T-G)

  • Each hyperparameter trial now resets trainer state (trainer = None) before running.
  • Prevents stale state leakage between trials.

• 🧍 ONNXRuntime C++ example gains pose support for YOLOv8-family pose models (PR #23786 by @chendao12138)

  • Adds pose tensor parsing, keypoint decoding/scaling, NMS for pose results, and visualization.
  • Supports FP32 and FP16 in the example pipeline.
  • Note: YOLO26 is not yet supported in this specific C++ example flow.

• 📘 YOLO26 training docs improved around MuSGD (PRs #23800, #23804 by @deriiinjv and @monkeyjack123)

  • Clearer explanation of when MuSGD is used with optimizer=auto.
  • Better practical guidance on when to try MuSGD vs standard options.

🎯 Purpose & Impact

• For deployment users on Rockchip 📦
  RKNN exports should now fail less often due to naming/path edge cases, making deployment workflows more dependable.

• For ML engineers tuning models 🔁
  Ray Tune trials are more isolated and reproducible, reducing hard-to-debug inconsistencies.

• For C++/edge developers ⚙️
  Easier starting point for pose inference in ONNXRuntime C++ projects using YOLOv8-style pose models.

• For YOLO26 trainers 🧠
  Optimizer behavior is easier to understand, helping users make better training choices faster.

What's Changed

• Reset trainer before each trial with Ray Tune by @Y-T-G in https://github.com/ultralytics/ultralytics/pull/23793
• Add YOLOv8 pose estimation support to ONNXRuntime C++ example by @chendao12138 in https://github.com/ultralytics/ultralytics/pull/23786
• Docs: Add explanation for when MuSGD optimizer is used by @deriiinjv in https://github.com/ultralytics/ultralytics/pull/23800
• docs: clarify MuSGD usage in training optimizer guide by @monkeyjack123 in https://github.com/ultralytics/ultralytics/pull/23804
• ultralytics 8.4.21 Fix Rockchip RKNN export path by @Laughing-q in https://github.com/ultralytics/ultralytics/pull/23806

New Contributors

• @deriiinjv made their first contribution in https://github.com/ultralytics/ultralytics/pull/23800
• @chendao12138 made their first contribution in https://github.com/ultralytics/ultralytics/pull/23786
• @monkeyjack123 made their first contribution in https://github.com/ultralytics/ultralytics/pull/23804

Full Changelog: https://github.com/ultralytics/ultralytics/compare/v8.4.20...v8.4.21